Why PFOA and PFOS Are Measured in Nanograms per Liter and What Four Decimal Places Mean
PFAS, or per- and polyfluoroalkyl substances, including PFOA and PFOS, are often reported in extremely small units such as nanograms per liter (ng/L), equivalent to parts per trillion (ppt). Measuring to four decimal places in these units is necessary because these compounds are present at very low concentrations that can still be meaningful for health and regulatory purposes. For example, detecting a sample with 0.0065 µg/L amounts to 6.5 ng/L, which is within the range government monitoring records track closely.
Which of the Fluorinated Compounds in Suffolk County’s Record Now Carry a 2024 Federal MCL and Which Do Not
The EPA has set federal maximum contaminant levels (MCLs) for some PFAS compounds effective in 2024. In Suffolk County’s public water system, PFOA and PFOS each have a federal MCL of 4.0 ng/L. Monitoring data from 2023 to 2025 found multiple detections of PFOA and PFOS above the reporting level of 0.004 µg/L (4.0 ng/L), with highest values reaching 6.5 ng/L for PFOA and 17.4 ng/L for PFOS. PFHxS carries a federal MCL of 10 ng/L, with one detection above that level. Other fluorinated compounds such as PFNA, HFPO-DA, PFBS, PFHxA, PFPeA, PFBA, and PFHpA currently do not have a federal MCL for Suffolk County’s water system but are monitored and reported.
How Public-System Records Differ from Private-Well Testing in What They Establish
The Suffolk County Water Authority serves over 1.1 million people through hundreds of thousands of connections with water sourced from groundwater. The EPA’s public water system records reflect broad regional sampling and provide insight into the general presence and range of PFAS in this water supply. However, these data do not measure the specific PFAS levels in an individual household’s water. Private wells may differ in composition, so the public records offer context but do not establish the exact condition at any one home.
The Order in Which to Rule Things Out, From Cheapest Check to Laboratory Test
If you are concerned about PFAS in your household water, start by reviewing your local public water reports available from the water authority. These documents provide a baseline of known regional water quality. Next, consider simple inline water quality indicators or filters targeting specific contaminants commonly found. For definitive assessment, a certified laboratory test is necessary. This test analyzes your home's water sample for specific PFAS compounds at precise concentrations, informing any further water treatment decisions.
What a Certified Laboratory Test for This Constituent Reports and How to Read It
A certified laboratory reports PFAS concentrations typically in nanograms per liter (ng/L, parts per trillion). The test results specify detections of individual compounds such as PFOA or PFOS with exact values. Understanding these results means comparing detected levels to federal guidelines or your own baseline preferences. Note that detection alone does not indicate a violation or unsafe condition; it is a measurement that helps guide treatment choices.
For households in Suffolk County seeking to address detected PFAS levels precisely tailored to their test results, the C-Series PFAS Forever Chemicals Filter ships ready to configure as an effective treatment option to reduce these 'forever chemicals' from drinking water.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2025-09-29. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR5 monitoring (2023-2025) for SUFFOLK COUNTY WATER AUTHORITY (NY5110526), NY: 4800 results across 10 listed contaminants, 169 detections above the reporting level; 33 results above a 2024 federal MCL